The long-term objectives of the Multiple Sclerosis (MS) Virology Program are to isolate, identify and determine the relationship of viral agent(s) to the disease, and to examine, using suitable model systems, parameters of the virus-host interaction which lead to chronic, progressive neurological disease. We have approached these problems from three major directions: (I) an analysis of human glial cell populations and their functions; only by an understanding of normal cell function can one begin to understand CNS pathology, (II) an attempt to isolate viruses which may be associated with MS: these include the use of "candidate" agents to elucidate the viral-cell interactions which may lead to CNS pathology and, (III) an examination of immune mechanisms, both cell-mediated and antibody-mediated, which might define the clinical symptoms of MS as an attempt by the body to repress viral infections.